Pharmacokinetic models are developed for the distribution and disposition of drugs, environmental contaminants and endogenous metabolites in animals and man. They provide a plausible set of equations that can be used to extrapolate from animals to man and thereby to improve chemotherapy and hemodialysis. BIBLIOGRAPHIC REFERENCES: Zaharko, D.S. and Dedrick, R.L.: Antifolates: In Vivo Kinetic Considerations. Cancer Treat. Rep. 61: 513-518, 1977. Bleyer, W.A. and Dedrick, R.L.: The Clinical Pharmacology of Intrathecal Methotrexate (NSC-740) I. Pharmacokinetics in Nontoxic Patients after Lumbar Injection. Cancer Treat. Rep. 61: 703-708, 1977.